The present invention pertains to an apparatus for singularizing and transferring preforms made of thermoplastic material, in particular polyethylene terephtalate (PET and polypropylene (PP), intended for use in applications requiring them to be subsequently blow molded into containers adapted to be filled with liquids of various kinds, especially alimentary liquids, beverages and the like.
Processes for production of such types of containers are generally known so as to be able to be schematically divided into two basic types, i.e. a single-stage process and a two-stage process.
In a two-stage process, a previously produced preform or parison, which is in a substantially amorphous state, is heated up again to its preferred molecular orientation temperature, at which it is then blow-molded into a desired shape. As used in this context, the term xe2x80x9ctwo-stage processxe2x80x9d or xe2x80x9cdouble-stage processxe2x80x9d, shall be understood to cover any process that produces a preform or parison which must then be heated up from ambient temperature to a related blow-molding temperature.
In contrast therewith, single-stage processes are so defined in that they are capable of forming the so-called preform, or parison, and transferring the preform from an injection mold or extrusion die (upon it having been allowed to cool down to some appropriate temperature) to a conditioning station, where it is allowed to evenly level at a temperature of preferred molecular orientation. The preform or parison is then transferred to a blow-molding die, in which it is finally molded into its desired form.
In particular, the present invention is particularly advantageous when it is associated with a preform manufacturing apparatus including a so-called two-stage plant for performing the two-stage process as defined above, but can be advantageously used also in conjunction with single-stage plants for performing the single stage process as defined above.
As a matter of fact, a need may arise in such types of plants for intermediate buffers or temporary storage units to be created as preform holding facilities, and cases in which this is required, as well as ways in which the buffers and related handling structure can be implemented, are exhaustively described in a detailed manner in Italian Patent Application No. PN97A000007 to ZOPPAS, to which reference is hereby made.
It is therefore a generally known fact that handling of preforms in view of subsequent processes and treatments must necessarily include a preform singularization step, i.e. a kind of operation in which the preforms are picked singularly from an initial container in which they are stored in bulk, in particular a rotary hopper, and are lined up along a transfer device from which the preforms can then be removed or collected in a desired quantity for subsequent processing or treatment steps.
Such a container is usually associated with a further apparatus that singularizes a preform, i.e. separates it from other preforms and prearranges it so as to be able to be sent or conveyed to an appropriate sliding or move-along line, and from this sliding line, which is essentially constituted by a simple groove delimited on both sides thereof by two guide and support rails provided in an arrangement that slopes down from an initial station to a final or terminal station, the preforms are able to slide along such a groove by simple gravity.
The preforms fit with a central portion of their cylindrical body into the groove and are supported by two side rails which intercept an upper rim or collar of the performs, immediately below threads on the preforms.
When so fitted in the groove, the preforms start to glide downwardly, in contact with each other, in an orderly sequence, so as to be appropriately prearranged for being picked up by suitable removal devices.
It has however been found, both experimentally and in practice, that such a method and related machines that carry it out, although simple and reliable, have a drawback that quite frequently forces the same machines to be stopped and be rearranged, i.e. reset manually. Accordingly, the machines have to be practically run under almost constant attendance of appropriate personnel.
Such a drawback, quite banal in its nature, is due to the fact that certain preforms, which are stored in bulk in the aforementioned initial container, may accidentally end up being inserted one within another. In particular, when the container is a rotary hopper, and, owing to possible impacts or pressures exterted upon the performs and friction between surfaces made of the same plastic material, the preforms are not able to be released from each other, i.e. separate from each other by themselves, but remain so stuck xe2x80x9cin pairsxe2x80x9d also in subsequent phases of the process.
In particular, these xe2x80x9cpairsxe2x80x9d of preforms stuck into each other are regularly singularized and loaded onto a sloping transfer line and, when they reach a terminal station where they are then picked up, they present themselves as a single preform that is almost double in its length.
Such a circumstance is detected by control devices provided for this purpose, which therefore respond by immediately and automatically shutting down the plant. To restore operation of the plant, and of course remove the preforms so stuck together, presence of an operator is required and this requirement, along with the production loss brought about by such a shutdown of the plant, gives rise to an additional burden that is neither predictable nor quantifiable.
Based on these considerations, it therefore is a main purpose of the present invention to provide an arrangement and a method concerning a preform transfer phase. Specifically, the arrangement and method are capable of doing away with the above cited drawback, so as to prevent overall plant productivity from being jeopardized, and which are capable of being easily implemented with aid of readily available techniques and devices, and therefore are reasonably low in cost and reliable and capable of being fully integrated with a preform production stage. The preform production stage may be provided upstream of the arrangement.
This aim, along with further features of the present invention, are reached in an arrangement for automatic removal of mutually associated preforms operating as recited in this specification.